We propose a study of age, sex and duration matched long-term diabetics (15 years or more), some of whom gave no evidence of diabetic retinopathy (controls), others with proliferative diabetic retinopathy (cases), in regard to the distribution of selected demographic systemic and ocular factors to determine if the distribution of any one particular, or any several of these factors, when taken independently or together is sufficiently different between the two groups to be considered a risk factor(s) or a protective factor(s) in the development of diabetic retinopathy. Patients will have an interview during which questions about medical and social factors possibly associated with the development of diabetic retinopathy will be asked. Patients will also have a standard eye examination, with stereo fundus photographs of seven standard fields taken to be used for classification of retinopathy. Those patients without visible retinopathy will have fluorescein angiography performed according to a standard protocol. Blood specimens will be drawn for analysis to evaluate systemic and metabolic factors that may play a role in the development of diabetic retinopathy. After all patients have been examined, photographed, interviewed, and had their laboratory evaluation, the data will be analyzed and estimations of relative odds for each individual variable studied will be computed. In addition, it is planned to look at combinations of variables as risk factors and to develop a multivariate risk function analysis of selected variables. Patients free of retinopathy (controls), will be followed prospectively at yearly intervals to evaluate the predictive value of the risk factors identified.